Turbo 1.4 TDI

1.4 TDI: from engine codes AMF and BHC to CUSA and CYZA – two generations of turbos with no interchangeable parts

The trap with the 1.4 TDI is a specific one: a Volkswagen Polo and an Audi A2 can both show 75 hp under the bonnet, yet require completely different turbos. The reason comes down to the engine code. The codes AMF, BAY, BHC, BMS, BNM, BNV and BWB cover the 70, 75 and 80 hp versions of the first generation, found notably on the Volkswagen Polo, Volkswagen Lupo, Audi A2, SEAT Ibiza, SEAT Cordoba and Skoda Fabia. The OEM references associated with these codes — such as 701729-5010S, 706680-5001S or 045145701 and its variants — cannot be carried over to later generations. Checking the reference stamped on the existing turbo, or verifying the engine code in the vehicle's documentation, remains the only reliable way to identify the correct part.

The shift to CUS and CYZ codes: 90 and 105 hp, entirely different references

The step up to 90 and 105 hp introduced a distinct family of engine codes: CUSA, CUSB, CUTA, CYZA and CYZB. These codes appear on vehicles such as the Audi A1, the Volkswagen Derby and the Skoda Roomster in their more recent variants. The corresponding OEM references — including the 04B253019 family and its derivatives — share no continuity with those for the AMF or BHC codes. The same vehicle, such as the Volkswagen Polo, exists across both generations: relying solely on the stated power output without checking the engine code will consistently lead to an incorrect order. It should be noted that certain codes such as CUSA or CUSB appear under several power outputs in the documentation: the OEM reference must always take precedence over the power figure alone.

Causes of failure and key points to check when replacing

On this small-capacity engine, turbo failure typically presents as an abnormal whistling noise, grey or black exhaust smoke, or a loss of power under load. The most common causes are insufficient lubrication — degraded oil or a blocked oil circuit — and fouling related to the diesel particulate filter or the EGR valve. A foreign body drawn in through the compressor can also destroy the CHRA. Addressing the root cause before fitting a new turbo is essential: fitting a replacement part without correcting the underlying problem will lead to a second failure. The new turbos listed on this page are sold as standard parts; reconditioned turbos, available for certain engine code combinations, are sold on an exchange basis.